In May 2009, seven astronauts aboard Space Shuttle Atlantis visited the Hubble Space Telescope for a final servicing mission. The drama of a shuttle flight with ambitious and challenging spacewalks that refreshed, repaired, and renewed astronomy's most beloved telescope captured the attention of the world. The underlying reason for such heroic efforts is to enable Hubble to perform new science. Yet, these new capabilities are easily lost in the excitement as the adventure unfolds. This episode aims to remind us of the ultimate value of such an amazing mission.

Hubble press release:

HubbleSite's Servicing Mission 4 page

Notes

This episode was filmed prior to the launch of the Servicing Mission 4, but was not posted for viewing until afterwards (we were kinda busy and absorbed in the proceedings during the mission). However, note that the content of the episode is not time sensitive, and speaks to the scientific capabilities that the mission enabled on Hubble. Both new instruments, Wide Field Camera 3 (WFC3) and Cosmic Origins Spectrograph (COS), were successfully installed. In addition, repairs to both the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS) were also successful.

The graph labeled "Hubble Survey Discovery Efficiency" is just one way to compare the capabilities of instruments on Hubble. You can find other comparisons, and each will have a slightly different focus and slightly different numbers for the improvements in the new instruments. No one number is definitive, but the sweeping generality that the new instruments enable Hubble to do significant new science can not be argued.

One can argue that after Servicing Mission 4, Hubble will be the best it has ever been -- not just in terms of the new instruments being better, but also in having more instruments operational. After launch, the telescope was hampered by the flaw in its mirror. Servicing Mission 1 installed COSTAR, the corrective optics, and that instrument has only now been removed during Servicing Mission 4. Hence, for 16 years, COSTAR has taken up an instrument slot, but not provided observing capabilities. If the NICMOS cooling system can be re-started, the observatory will return to its full capabilities with five science instruments.

Many people have asked: given the improvements that WFC3 and COS will provide over ACS and STIS, why did we need to repair the older instruments? There are several answers. First, there is great value in redundancy. As we will not be able to return to Hubble once the space shuttle fleet is retired, having working backups in the event of a failure is a prudent move. Second, the older instruments are well-calibrated and familiar to scientists. Astronomers may choose to utilize the known instrument to speed-up their research or to retain consistent data processing as earlier observations. Third, the older instruments have different and complementary capabilities to the new instruments. The design of each instrument involves trade-offs, and each is optimized for a particular range of observations. Some observations can best or only be done with the older instruments, as they were optimized for that type of observing.